1. Field of the Invention
The present invention relates generally to a camera provided with a photoelectronic line sensor scans a document lying on a support surface line-by-line and generates electrical signals. The line sensor comprises a plurality of image detection elements arranged in a line.
2. Description of the Related Art
In known devices to scan a document, light-sensitive cells are linearly arranged in a line in order to determine (with the aid of an electrical signal) the intensity of the light impinging on these light-sensitive cells. Such light-sensitive cells can, for example, be CCD sensors (charge coupled device) that are fashioned as one- or two-dimensional CCD sensor arrangements. At least the line of the document to be scanned is illuminated with the aid of a light source. The light reflected by the document is supplied to the image detection elements of the CCD line sensor. The image detection elements generate an electrical charge corresponding to the supplied light.
After the detection of one line, the charge quantity of each image element is determined, in that the stored charge is, for example, supplied to an analog-digital converter. Either the document and/or the scanning device is subsequently shifted such that the next line can be scanned. Such devices for scanning a document are also designated as scanners that can, for example, be executed as flatbed scanners, hand scanners or drum scanners. In such known scanning devices, a document is illuminated in lines, whereby a camera records graphical elements of the document line-by-line and subsequently generates image data that are subsequently further processed. The width of the support surface and the number of the linearly arranged image detection elements define the resolution with which the image elements of the line of the document to be scanned are recorded.
Depending on the document to be recorded, different requirements are placed on the resolution with which the document should be recorded. It is thus frequently necessary that photos must be recorded with an optimally high resolution, however text can be recorded with a lower resolution. Thus in the prior art it is known to scan only every second possible line of the document. The scanning speed of the document can thereby be nearly doubled. Depending on the application field, the requirements for the image quality and the scanning speed can vary quite significantly. Thus in general a high scanning capacity at lower image quality, i.e. at lower resolution, is opposite to a lower scanning speed with higher image quality. Known devices to scan a document can react to these different requirements only in a limited manner. An adaptation to the different requirements can, for example, ensue via the exchange of the optoelectric line sensor and the associated optics. However, this exchange is connected with a large technical and financial expenditure.
An image reader in which an image to be recorded is recorded with the aid of a CCD image sensor is known from German Patent Document DE 30 39 139 A1. The light reflected by the document is deflected to the image sensor with the aid of a mirror. The deflected light is focused on the image sensor with the aid of an objective.
From German Patent Document DE 41 43 483 C2, a document reader is known that scans a document over a predetermined scan width along a primary scanning direction with the aid of a light beam. The light reflected by the document is detected with a photoconductive device. The reflected light is imaged with the aid of an objective on the photoconductive device.
From the Japanese Patent Document JP 7-30729 A it is known to image the light reflected by a document on two sensor elements with the aid of a lens and multiple reflection elements. The sensor elements respectively have a different pixel count per length unit with which they detect the light reflected by the document.
From the Japanese Patent Document JP 7-135556, it is known that the signals of multiple sensor elements of a sensor line are averaged to record the light reflected by a document corresponding to a target resolution that is less than the physical resolution of the sensor element.
From the Japanese Patent Document JP 5-68140 A, a line sensor is also known that can be read out twice as fast with halved resolution. A mechanical movement of the optics that image the light reflected by the document onto the sensor element is not necessary.
From the Japanese Patent Document JP 2000-354158 A, an adjustable optic is known via which documents with different width or with different resolution should be scanned, imaging the light reflected by the document onto the line sensor in a suitable manner. The respective width of the document is then imaged onto the available width of the sensor with the aid of the adjustable optic.
Further image generation devices are known from the documents U.S. Pat. No. 6,219,463 B1, European Patent Document EP 1 126 692 A and U.S. Pat. No. 6,215,563.